Beginning to build the Mega Der Red Max (Estes PS II). Kit comes with 12 sheets of 3/32" x 12" x 4" balsa sheeting for the fins. (Laser cut 1/8" plywood makes up the fin cores.) The instructions show two 3/32" sheets butt glued (long edge) used to sheet one side of each fin. If you're a BAR like me, then you probably started to layout the sheets and fin cores to see how many sheets it takes to cover the three cores on one side (being a balsa "Scrooge"). The answer is five. However, this causes one of the three fins to have two butt edge seams (instead of one per Estes instructions). See my photos, attached.

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How dense are those sheets of balsa in your kit? Mine averaged about 16 lbs. per cubic foot (the stack of 12 sheets weighed just over 9 ounces). I was surprised that the edges of the sheets were generally straight enough that the butt joints went pretty well without much sanding.

I'm doing fillets and such on mine at the moment.

This being my first four-inch rocket I'm fairly amazed by the size of the thing.

I'm also finding that my preliminary OpenRocket sim is giving altitudes on the order of 1000 feet on a G80...twice what the package advertises. I thought 500 feet seemed awfully low for this when the Leviathan does close to 2000 feet.

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Bernard Cawley
NAR 89040 L1 - Life Member
SAM 0061
AMA 42160
KG7AIE

I'm thinking of converting mine to 38mm motor. I just need to figure out whose 4" x 38mm rings are the best fit for the Estes tube. I am not convinced I could re-drill the included rings and keep the motor straight.

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Member: Washington Aerospace Club NAR Section #578
NAR #94383
TRA #15009
HPR Level 2

Order custom rings from BMS - they're not expensive and nicely made (laser cut). You probably would have to cut the slots for the fin tabs in the middle ring by hand, but that's doable.....

I used BMS to get baffle plates to make a two-tube style baffle assembly for the Mega DRM.

__________________
Bernard Cawley
NAR 89040 L1 - Life Member
SAM 0061
AMA 42160
KG7AIE

Great thoughts from my responders (above)! I have included photos of the three fins sheeted on one side. I too found the balsa to be hard and of good quality, requiring no sanding before gluing the butt edges (which I accomplished with thin CA). I'm using Elmer's Carpenter's Wood Glue to glue the sheeting to the cores. I am weighing them flat with a car battery with a piece of 1" high density foam as a cushion.

Secondly, I have attached the design of the Cap-tain ejection baffle system which is very light and requires only one additional centering ring. I have used it with great success for over ten years.

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Randy G.
NAR 15345 L1
Flying rockets since 1967.

I find from my Jolly Logic Two that I get about 500 feet on an F40-4 in a four inch Das Blue Max I have been flying for years (the models are nearly identical). I don't find your sim' surprising when it predicts 1000'.

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Randy G.
NAR 15345 L1
Flying rockets since 1967.

Well, it's 1063 feet on a G80. It's predicting 646 feet on the F50. I can't quite get OR to give me the right nose cone shape, so the one in the sim is a little slimmer.

I used measured kit component weights but haven't yet compensated for glue or the as-yet unapplied finish. It looks like, bare, it's going to come in just at or very slightly under the face card's weight of 31 ounces (it's at about 30.8 now). How much does your Das Blue Max weigh?

I expect to be putting a Jolly Logic altimeter aboard when I fly mine as well.

__________________
Bernard Cawley
NAR 89040 L1 - Life Member
SAM 0061
AMA 42160
KG7AIE

I weighed Das Blue Max and it was 31.25 oz. dry w/'chute. This rocket has "tons" of paint on it as it's been repainted three times (total) now.

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Randy G.
NAR 15345 L1
Flying rockets since 1967.

The fins have warped. Not from root to tip, but from leading edge to trailing edge (which would cause the rocket to spin). I tried leaving them under a heavy object for days after wetting them thoroughly with water and isopropyl alcohol. I thought that worked and sat them aside to find them warped again.

Thinking about applying epoxy to both sides and then sandwiching with a weight (with appropriate non-stick barriers, of course).

Any suggestions?

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Randy G.
NAR 15345 L1
Flying rockets since 1967.

Randy,

What I have done before with success is to use CA. For this case, I would soak down one side of the balsa with thin CA, then quickly lay it on some Saran wrap or equivalent, the weigh it down until it is dry. Do the same to the other side. The thin CA is, essentially, liquid plastic and will fill the grain; this filling should lessen or eliminate the warp if the fin is laid on a truly flat surface and weighed down enough. The Saran keeps it from being glued to the weight (or the table).

It's warped because of moisture content in the white or yellow glue you used to glue balsa sheets to the framework of the fins.

I used thick CA on the frame when gluing mine up which allows some 'wiggle time' to make sure the balsa pieces are straight and like you want them. Then you set the assembly under weight to keep things straight as they cure. Then do the other side.

Worked super. I will use epoxy to glue mine into the TTW BT and engine mount. I will use epoxy for the fillets, as well.

Good luck!

Allen